6-O-methylerythromycin A (clarithromycin), shown below, is a potent macrolide antibiotic disclosed in U.S. Pat. No. 4,331,803. 
In general, the process for making clarithromycin can be thought of as a four-step procedure beginning with erythromycin A as the starting material:                Step 1: optionally convert the 9-oxo group to an oxime;        Step 2: protect the 2′ and 4″ hydroxyl groups;        Step 3: methylate the 6-hydroxyl group; and        Step 4: deprotect at the 2′, 4″ and 9-positions.        
A variety of means for preparing 6-O-methylerythromycin A have been described. 6-O-methylerythromycin A can be prepared by methylating a 2′-O-3′-N-dibenzyloxycarbonyl-des-N-methyl derivative of erythromycin A•(U.S. Pat. No. 4,331,803). 6-O-methylerythromycin A can also be made from 9-oxime erythromycin A derivatives (See, e.g., U.S. Pat. Nos. 5,274,085; 4,680,386; 4,668,776; 4,670,549 and 4,672,109, U.S. Pat. No. 4,990,602 and European Patent Application 0260938 A2).
In those reports relating to 9-oxime erythromycin A derivatives, the oxime is protected during methylation with a 2-alkenyl group (U.S. Pat. Nos. 4,670,549 and 4,668,776), a benzyl or substituted benzyl group (U.S. Pat. Nos. 4,680,386, and 4,670,549) or a moiety selected from the group consisting of lower alkyl, substituted alkyl, lower alkenyl, aryl substituted methyl, substituted oxalkyl, substituted thiomethyl (U.S. Pat. No. 4,672,109), and ketal group (U.S. Pat. No. 4,990,602).
There continues to be a need to provide a rapid, efficient method of producing 6-O-alkyl erythromycin compounds that uses mild, neutral synthetic conditions and to provide novel intermediates useful in the production of 6-O-alkyl erythromycin derivatives.